ISSN 10227954, Russian Journal of Genetics, 2010, Vol. 46, No. 8, pp. 932–937. © Pleiades Publishing, Inc., 2010.
Original Russian Text © O.E. Mel’kina, I.V. Manukhov, G.B. Zavilgelsky, 2010, published in Genetika, 2010, Vol. 46, No. 8, pp. 1050–1056.
Energydependent degradation of proteins in
bacteria occurs under the action of
ATPdependent proteases (Lon, Clp, FtsH, etc.).
These proteases help to eliminate denatured (abnor
mal) proteins or proteins misfolded in the process of
synthesis from the cell. They also play an important
role in some regulatory cascades, for example, in the
transition of cells into the stationary phase, in the heat
shock, etc. [1–3].
In the sea bacteria
, the expression of
genes is regulated by the LuxILuxR system
that determines the intensity of bioluminescence of
growing cells depending on the population density
(quorum sensing): the absence of luminescence at low
cell concentrations and a sharp intensification of
luminescence at a critical population density [4–6].
of two operons:
promoter [7, 8]. The
genes encode the regulatory proteins LuxI and LuxR.
Acyl synthase LuxI is involved in the synthesis of an
autoinducer (AI), which is an acylic Lhomoserine
lactone derivative N(3oxohexanoyl) Lhomoserine
lactone . This autoinducer plays a crucial role in the
communication of bacteria, as it freely diffuses
through cell membranes . The LuxR protein is a
positive regulator (activator) of transcription of the
operon. The LuxR protein bound to AI
forms a complex with the
box representing an
inverted 20 bp repeat in the
promoter region and
activates transcription of the
It is of interest to analyze the role of ATPdepen
dent proteases in the regulation of quorum sensing
is a suitable
model for such analysis, because the efficiency of
expression of the
operon genes is estimated by the
intensity of bioluminescence and the
can be cloned in
mutant for proteaseencoding genes. We showed ear
cells mutant for the Lon protease
and carrying a plasmid with the
are characterized by an
increased level of bioluminescence even at cell con
centrations significantly lower than the critical value
. Here, the influence of the ATPdependent pro
teases of the Clp family (ClpAP, ClpXP) and Lon on
the expression of the
regulon genes is
analyzed. The influence of AI on the activity of ATP
proteases as negative regulators of
MATERIALS AND METHODS
Bacterial strains and plasmids.
and AB1899 (from the collection of the State Research
Institute of Genetics and Selection of Industrial
; AB1899 F
, other markers as in
the case of AB1157.
remaining markers as in the case of AB1157 ) were
obtained from Professor N. E. Murray (Institute of
Cell and Molecular Biology, University of Edinburgh,
(the remaining markers as in
the case of SG22163) as well as
lacU169 araD flbB relA clpA+
(the remaining markers as in the case of
SG20250 ) were obtained from Professor S. Got
tesman (National Cancer Institute, Bethesda).
Proteolytic Control of Expression of
O. E. Mel’kina, I. V. Manukhov, and G. B. Zavilgelsky
State Reseatch Institute of Genetics and Selection of Industrial Microorganisms, Moscow, 117545 Russia;
Received February 2, 2010.
—The key elements of the regulatory system activating expression of the
operon genes in the
are the LuxR protein (an activator of transcription) and N(3oxohexanoyl)
Lhomoserine lactone (an autoinducer, AI). It is shown that the ATPdependent proteases ClpXP and Lon
take part in the negative control of expression of the
operon genes and that AI protects the LuxR protein
GENETICS OF MICROORGANISMS